The invention relates to a lens testing device. Such a testing device is disclosed in the printed publication Patents Abstracts of Japan JP-A-09159575.
Measurement of the modulation-transformation function (MTF) is the quantitative method most frequently used to assess the optical imaging quality of photographic objectives and optical systems of related type. An objective testing device suitable for this purpose is known, for example, from Optical Shop Testing, edited by Daniel Malacara, published by John Wiley and Sons Inc., Second Edition, (1992), page 421. A slit illuminated from the rear or a hole (point) is projected to infinity using a collimator objective. The objective specimen images the slit or the hole in its focal plane. As a rule, the collimator focal length is greater than that of the specimen, with the result that there is a demagnifying imaging which can only be evaluated after remagnifying with the aid of a microscope objective.
The same operating principle is used by focal length measuring instruments in which the slit is replaced, for example, by a double slit. The focal length of the specimen can be determined by measuring the magnification of the double-slit image.
In order to measure the imaging properties (MTF) or the focal length (distortion) in the image field (image heightxe2x89xa00), the specimen must be pivoted, in accordance with the angular field, and the remagnifying microscope objective must be tracked relative to the image point.
An objective testing device suitable for this purpose is described in DE 38 42 144 A1. A test pattern illuminated from the rear is imaged to infinity via the exit lens of an illuminating device. The illuminating device can be pivoted relative to the specimen. The specimen is supported rotatably about its optical axis. The image of the test pattern produced by the specimen is imaged via a microscope objective onto a flat CCD array and evaluated via an image processing system. The image-recording device is arranged displaceably perpendicular to the optical axis of the specimen.
A testing device for an afocal optical system is disclosed in Patent Abstracts of Japan JP-A-09281002. An afocal objective is provided as specimen. The illuminating device and the detector device can be pivoted relative to the specimen.
The above mentioned Patent Abstracts of Japan JP-A-09159575 discloses a lens testing device in which the specimen images the test object illuminated from the rear directly into an intermediate image plane from which it is imaged via an imaging objective onto a detector device. This specimen is supported rotatably about its optical axis. The imaging objective and the detector device are combined to form a unit and fastened on a stand. The illuminating device with the test object, and the holder for the specimen are respectively combined to form further units which are likewise fastened on the stand with a fixed alignment relative to one another.
An object testing device is disclosed in Leitz-Mitteilungen fxc3xcr Wissenschaft und Technik, (1970), volume V, issue 1, pages 3-12, FIG. 5.
U.S. Pat. No. 5,221,834 discloses a control device for an imaging system, for example, a lens in which the local optical transfer function is determined.
The two-stage imaging present in the known devices necessitates a high technical outlay which, in the case of MTF applications, is reflected in the three-dimensional space requirement, in particular. The measuring accuracy depends very strongly on the imaging quality of the microscope objective. For measurements in the image field, the requirements placed on this relay optical system are particularly high, since the aperture is used only partially because of the measurement principle.
Object of the invention was to develop a lens testing device of universal applicability for different tests made on photographic and video objectives, which has a compact design and whose measuring accuracy is improved.
According to the invention, in the case of a lens testing device of the type mentioned at the beginning, this object is achieved by virtue of the fact that the lens specimen is an objective specimen, the test object is arranged in the focal plane of the objective specimen inside the holder, the imaging objective is a collimator objective, the detector device being arranged in the focal plane of the collimator objective, that either the holder or the unit is pivotably supported on the stand, and the holder and the unit can be pivoted relative to one another. The result of this is a single-stage, magnifying imaging of the test object. The image can be evaluated via an observing device. For measurements in the image field, either the holder can be pivoted with the specimen, or the unit can be pivoted with the observing device. It is advantageous when the test object is adjustably arranged inside the holder relative to the plane of the mount of the objective specimen.
For further measurements in the image field, the mount of the objective specimen is rotatably supported in the holder. It is possible to provide as an observing device a CCD camera whose recorded image can be fed to a monitor for visual assessment. For the purpose of automatic assessment of measurements it is possible to connect downstream an electronic image evaluating device which carries out the evaluation of measurements with the aid of image analysis methods.